Hi Jungleexplorer,
it will be handy, if you provide us your system specification.
Make sure u have at least 60Gb free on your hdd and nothing running on the back ground..
like antivirus..that saves alot time.
i have made iso,drivers with all the version of wintoolkit and only once crashed
i'm running windows 7 x64 sp1 16GB Ram
you shoud also understand, that the iso image is unpacked and repacked(Rebuild), that's
why the image is large

Which version of windows 7 are you using?
this error can occurred , if u use wrong updates on wrong os
example: windows 7 and x64 updates.......don't mix them
check that you're using the right updates, with the right os.
Also update your os often and install runtimes,net, drivers